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Canadian Journal of Cardiology

DETERMINING THE ROLE OF VON WILLEBRAND FACTOR IN THROMBOTIC POST-TRANSPLANTATION COMPLICATIONS USING EX VIVO LUNG PERFUSION SYSTEM

      BACKGROUND

      von Willebrand factor (VWF) is a pro-coagulant glycoprotein expressed only in endothelial cells and megakaryocytes. It plays a critical role in hemostasis and thrombus formation. It mediates the adhesion of platelets to the endothelium/sub-endothelium surfaces, which is the primary step in thrombogenesis. Our previous analyses demonstrated that hypoxia induced an increase in levels, and alteration in vascular tree expression pattern, of the VWF specifically in the lungs of mice. Alteration in expression pattern corresponded to a significant increase in the proportion of lung microvascular endothelial cells that exhibited de novo activation of VWF expression. Hypoxia-induced elevated and altered VWF expression was correlated with a significant increase in platelet aggregates formation in the lung vasculature. Since during organ-transplantation donor organs are under hypoxic conditions, we explored whether this may lead to alterations in VWF expression and whether modification of transplantation procedure to reduce hypoxic exposure could prevent such alterations.

      METHODS AND RESULTS

      Procured pig's lungs that were maintained in static cold storage “SCS” or exposed to ex vivo lung perfusion (before and after perfusion) were used. Lung tissue biopsies were obtained immediately after organ harvest, 12 hours post cold storage, or post warm perfusion. VWF RNA and protein expression levels were analyzed using RT-PCR and western blot. In addition, we proceeded to determine whether SCS preservation also alters the proportion of pig's lung vascular endothelial cells that exhibit VWF expression. For these analyses, we performed double stained immunofluorescence (IF) analyses using CD31 (endothelial cell marker) and VWF antibodies on samples of lungs that were preserved and transplanted. Results demonstrated that VWF mRNA and protein levels were similar after 12 hours of cold storage compared to immediate harvest, but were significantly reduced in lungs that were perfused under ex vivo lung perfusion “EVLP” for 12 hours. Furthermore, IF analysis demonstrated that preservation of lungs under cold storage conditions prior to transplantation altered VWF expression pattern leading to an increasing number of microvascular (indicated by CD31 staining) endothelial cells that express VWF.

      CONCLUSION

      Increased VWF expression in microvascular endothelial cells under SCS may contribute to transplant associated thrombogenicity. Reduction of VWF expression through ex vivo normothermic perfusion may have a significant effect in reducing potential thrombogenic consequences, which is a major complication of organ transplantation.
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